The Complete Mitochondrial Genome of Endemic Freshwater Sculpin Cottus dzungaricus (Scorpaeniformes: Cottidae) Revealed by High-Throughput NGS: Genome Structure and Its Phylogenetic Relationships

Cottus dzungaricus is an indigenous and infrequent cold-water sculpin in Irtysh River China, the classification status was still controversial. In this study, a total of 16,530 bp circular and double-stranded Cottus dzungaricus complete mitochondrial genome was sequenced. The average nucleotide composition showed a slightly higher AT content and strong anti-G bias. Selective pressure tests of 13 protein-coding genes revealed only Cyt b gene experienced the positive selection. The mean genetic distances (0.018-0.123) showed various interspecific divergences within genus Cottus. The NJ phylogenetic tree based on K2-P model fell into two major lineages, one of which was further divided into two sublineages. These three clusters of cottoid fishes might respectively represent different salinity adaption types. Combined with their geographical distribution pattern, we speculated that genus Cottus originated in the Far East and C. dzungaricus was a transitional or intermediate species during the population dispersion. The controversial classification status of C. dzungaricus was also discussed by reconstructing a dendrogram based on mtDNA control region. The conclusions will lay the foundation for clarifying the classification relationship of genus Cottus.